A typical shutter mechanism of the prior art includes an electromagnet comprising a ferrite core surrounded by a magnetic winding on a pancake bobbin and also includes a very thin elongated flexible foil steel strip attached by retaining screws at one end to a collar and lying parallel to and below a laser beam path when the electromagnet is inactive. In operation, the winding is energized, activating the magnet and causing the free end of the foil strip to be attracted to the magnet and bend upward into the beam path. As the end of the strip intercepts the beam path, the beam is reflected away from the path by a few degrees. The angle of reflection increases as the foil end approaches the magnet. In the fully closed position the strip conforms flat against the magnet and then bends sharply downward to the retaining screws, blocking the beam.
The foil strip is not only extremely flexible, but also has low mass which aids in reducing vibration caused by the collision of the strip with the electromagnet. However, the strip is also very weak, particularly at stress points in the bend, and thereby has a lifetime of only about 100,000 cycles before breakage occurs. The strip reflects the beam at an angle near that of the unaltered beam path, creating an unwanted stray reflection line that must be trimmed off. The orientation of the strip in the fully closed position allows laser light to be scattered back into the laser, preventing its use in certain applications. Thermally, the thin foil is not capable of conducting away sufficient heat arising from absorption high power laser light.
In U.S. Pat. No. 4,332,450 Griffith discloses a magnetically actuated optical shutter in which a magnetic field is provided in an air gap defined by a pair of poles of an electromagnet and a magnet is provided in the air gap with its field oriented at an angle to the first magnetic field. A lever pivoted about an axis entirely outside of the air gap and extending through one of the electromagnet's poles carries the magnet. An optical aperture is positioned in a path of the lever for selective obstruction by the lever. Interaction of the magnet with the magnetic field defined by the electromagnet causes the lever to pivot into or out of a position obstructing the aperture, thereby causing the lever to act as an optical shutter.
In U.S. Pat. No. 4,415,231, Kaczensky et al. disclose a "fail-safe" radiation shutter which includes a housing through which a defined beam path extends, two independently operated electromagnetic shutter devices arranged one behind the other relative to the beam path to intercept or pass the beam, and means for blocking the beam path with one of the shutter devices when a failure is sensed in the other. Each shutter device comprises a diaphragm or filter element fastened to the free end of a pivotally supported swivel arm and an electromagnetic actuator, such as a solenoid, arranged for tilting the swivel arm into a beam passing position. A spring fastened to the swivel arm returns the arm to a beam blocking position when the actuator is turned off.
An object of the present invention is to produce a laser beam shutter mechanism having long life and no stray reflection so as to be suitable for high speed pulse operation.
Another object of the present invention is to produce a shutter mechanism suitable for use with high power lasers and other beam sources.
A further object is to produce a shutter mechanism with smaller and thinner packaging so as to enable its use in application with tight space requirements.